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What have you been told already about HD and the reason you were referred to see us?

Wondering what questions or concerns you might like to discuss with us today?

How has your diagnosis of a neurodegenerative disorder changed your life the most?

Since HD is usually passed on by a parent I like to begin by taking a family medical history to see if any other family members may have had symptoms of HD. Sometimes HD can be misdiagnosed as something else like Parkinson's or Alzheimer's disease because they share some of the same symptoms and other times family members have passed away before symptoms of HD develop

We can then discuss the cause of HD and details about the genetic testing we have to offer you.

Dr. ____ will also be in later to perform a short physical examination and further discuss HD

In the late stages of HD, behavior problems are gradually lessened, but motor disability becomes severe and the patient is often totally dependent, can't speak, and can't control bladder function, weight loss often becomes a concern

Disease usually progresses slowly over a 15-20 year period after which death occurs

In order to understand what causes HD and to understand the testing for HD it is helpful to review some genetics

Review chromosomes, genes, DNA, nucleotides

Gene IT-15 (discovered in 1993)

located on chromosome 4

area in the gene where there are tri-nucleotide repeats

Most individuals have between 9 and 26 repeats

Alleles of 27-35 CAG repeats are considered intermediate alleles. A person with an allele in the intermediate range do not develop HD, but they may have children with HD if the number of repeats increases when the gene is passed on

An allele in the range of 36-41 is associated with reduced penetrance for symptomatic HD (they may or may not develop symptoms of HD)

The HD gene produces a protein (Huntingtin)

widely expressed

function unknown

CAG expansion causes altered structural and biochemical properties

The protein has been shown to accumulate in neurons within the brain

Uncertain if this accumulation is what causes symptoms

Inverse correlation between CAG repeat length and the age of onset

Patients with adult onset of symptoms usually have an expansion that ranges from 40-55 CAG repeats

Patients with juvenile onset of symptoms usually have expansions about 60 repeats

Repeat length does not correlate with any other clinical feature, exact age of onset, or rate of progression

Diagnosis of HD rests on a positive family history, characteristic clinical findings, and molecular DNA testing the reveals an expansion of the CAG repeat in the HD gene

Imaging studies including MRI, CT, SPECT, and PET may provide additional support for the clinical diagnosis. (used mainly to determine whether other conditions are contributing to the neurologic dysfunction)

There are alternative reproductive options for those not wishing to risk transmitting the disorder to offspring

Prenatal testing is possible using DNA that has been extracted via amniocentesis or chorionic villus sampling (CVS).

Preimplantation genetic diagnosis (PGD) is also available. This technology uses in vitro fertilization (IVF) to produce embryos, which are tested for the HD mutation. Only embryos without the CAG expansion are implanted into the uterus.

You can have this procedure done without knowing if you actually carry the mutation